Generating a non-reproducible printed image

ABSTRACT

A method of generating a non-reproducible printed image, for example on a check, involves printing a first, background layer of ink on the document, and then printing data on top of the background layer. The ink used to print the background layer is reflective of light of a predetermined wavelength, typically in the infra red spectrum. The ink used to print the data is visually indistinguishable from the first ink, but absorbs light in the infra red spectrum, so that when the printed image is illuminated with infra red light, the image can be discerned. The image typically comprises an encrypted symbolic image and is used for security purposes.

BACKGROUND OF THE INVENTION

This invention relates to a method of generating a non-reproducibleprinted image which can be utilised in the production of documents whichare not to be copied.

Valuable documents such as cheques, vouchers, identification documentsand the like are subject to fraudulent copying, and various schemes havebeen adopted in order to make such copying difficult. However, as thetechnology available to counterfeiters becomes more sophisticated, it isnecessary to adopt more and more sophisticated measures to preventunauthorised copying of such documents.

SUMMARY OF THE INVENTION

According to a the invention there is provided a method of generating anon-reproducible printed image, comprising the steps of:

-   -   applying a first, background layer of an ink which reflects        light of a predetermined wavelength or range of wavelengths to a        substrate; and    -   printing the image on the background layer using an ink which        absorbs light of the wavelength or range of wavelengths.

The wavelength or range of wavelengths may be in the infrared spectrum.

The substrate may comprise sheet material such as paper, card or anothergenerally planar material.

For example, the substrate may be a sheet of paper, a card or tag, alabel, a ticket, an identification plate, or any other article to whichthe ink can be applied.

The image may be a bar-code or symbolic image, preferably atwo-dimensional encrypted bar-code or symbolic image.

The invention extends to apparatus for reading the non-reproducibleprinted image printed by the above defined method, the apparatuscomprising:

-   -   a camera;    -   a filter for filtering an image captured by the camera at a        predetermined wavelength or range of wavelengths; and    -   an illuminator arranged to illuminate the non-reproducible        printed image with light at said wavelengths or range of        wavelengths, so that infra red light reflected by the first,        background layer of the printed image is passed by the filter,        permitting reproduction of the image by the camera.

Preferably, the filter comprises an infra red filter and the illuminatorcomprises an infra red light source.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows data corresponding to an image generated according to theinvention, in a text string format;

FIG. 2 shows the image as printed; and

FIG. 3 shows apparatus of reading the image.

DESCRIPTION OF AN EMBODIMENT

The present invention will be described with reference to a practicalapplication in the safeguarding of paper documents which have monetaryvalue, such as cheques or vouchers. It will be appreciated that thedescribed embodiment is purely exemplary, and that the invention hasapplication in other areas as well. In particular, the invention is notlimited to use with paper documents, but can be used in conjunction withother substrates such as, for example, credit cards or identificationcards, drivers licenses, certificates, share certificates, banknotes,labels, identification plates or tags.

In the prototype application, a system was required to prevent chequesand vouchers from being created illicitly, and to prevent printedcheques and vouchers from being duplicated. It was also required tostore information on the drawer of the cheque, to incorporate uniqueserial numbers for each cheque for use in making enquiries on thedrawer's cheque/voucher printing database, and to carry accountabilitydata on the cheque. It was also required to incorporate verificationdetails of an authorised bearer or holder of the cheque in thenon-reproducible image printed on the cheque.

To achieve this, a “data watermark” was designed which can be printed onthe paper of the cheque or voucher but which cannot be copied. Withinthe watermark image is machine readable symbolic data, comprisingsymbols which can be acquired by a computer and decoded or interpretedinto data which can be processed by the computer in a conventionalmanner. These symbols are a printed symbolic representation of computerdata which is encrypted prior to the creation of the symbols. Thesymbols are extracted in use from the non-reproducible image orwatermark by means of a specific imager designed for this purpose.

The first step in the creation of cheques or vouchers according to themethod of the invention is the preprocessing of a batch of blank chequesor vouchers with a first, background layer of ink. A block is printed ina predetermined area of the cheque or voucher using an ink which ishighly reflective in the infra red spectrum in the 800 nm to 975 nmrange. This spectrum corresponds to the spectrum of the infra redradiation emitted by an LED scanning device used to read the cheques.The ink appears black when illuminated by visible light, but has littleor, preferably, no carbon content. If the background ink contains even asmall amount of carbon, this will reduce the reflectivity of the ink tothe infra red spectrum, resulting in a lack of contrast between thebackground ink and the second layer of ink printed on top, which isinfra red-absorbing. Ideally, the background ink has no carbon content,while the foreground ink has a high carbon content.

Most black inks use a high proportion of carbon in order to render themdark. However, it is possible to make use of a mix of pure dark colourswhich have no carbon in them in order to obtain a “clear black”. Forexample, a colour mix comprising equal proportions of dark non-carbonbased pure colours such as red, green and blue or cyan, magenta andyellow can give a dark shade of grey which is suitable for the abovepurpose. Certain existing computer printers and plastic card printersare available that make use of inks which are non-carbon based and whichare highly reflective in the infra red part of the spectrum. Certaincolour ink jet printers, such as the Epson stylus (trade mark) printersmake use of non-carbon based inks.

Before a cheque or voucher is printed, it is necessary to capture therelevant data which is to be represented thereon. This includes detailsof the drawer of the cheque/voucher, the payee, the date and the amount.This data is sent to a compression software program as an input file,and is read and compressed so that more data can be represented by twodimensional symbols or barcodes which occupy a relatively small physicalarea. The compressed data is then processed by a forward errorcorrection program which adds parity information to ensure that lostdata can be recovered if the two dimensional barcode or image isdamaged. This software utilises the Reed-Solomon methodology of creatingforward error correction in data streams.

The data is now processed into symbols which form the readablerepresentation of the data. Unlike known two dimensional barcodes whichare created as a bit map image, the symbology utilised is a set of ASCIIstrings. The letters in the string are interpreted by a speciallycreated font file and thus are converted to symbols when printed. Thismethod was adopted as bitmap images occupy large amounts of memory andtend to significantly slow down the printing process utilised by theprinters of cheque books. FIG. 1 shows a sample of a two dimensionalbarcode in a text string format.

When the data shown in FIG. 1 is printed via a specially created “TrueType” (trade mark) font set file which interprets the text string intotwo dimensional barcode symbols, the resulting image as shown in FIG. 2is obtained.

Once the text string representation of the 2D barcodes has been createdfor each cheque in a cheque book, it is loaded to the printer buffer andthe two dimensional barcode is printed on the cheque. The twodimensional barcode or image is printed over the infra red reflectivebackground ink utilising a laser printer (or other conventional printer)which makes use of carbon based black ink. This means that the printedimage is substantially invisible under visible light. Such ink isabsorbent of infra red light, so that the infra red responsiveness ofthe background ink is inhibited wherever the symbols are printed on topof it.

Most if not all laser printers as well as thermal transfer printers makeuse of inks which have a very high carbon content. In commercialprinting such as offset printing, most Pantone colour mixes which aredark or near black have a high content of carbon.

The apparatus used to read the data in the printed image or barcode isshown FIG. 3, in a highly simplified schematic form. In FIG. 3, a highresolution CCD camera 10 is shown which is arranged to scan a twodimensional barcode 12 on a cheque or voucher 14 when the latter ispositioned correctly. A set of light emitting diodes 16, which may bearranged in a ring around the lens 18 of the camera 10 direct infra redlight onto the cheque or voucher 14. Reflected infra red light passesthrough an infra red filter 20 mounted in front of the lens 18 beforeentering the camera. Other light is rejected.

Since the background ink used to print the image 12 is highly reflectivein the relevant frequency range, particularly in the range 850 nm to 900nm, light from unprinted portions of the symbol is reflected and sensedby the CCD camera. The foreground ink printed over the background inkand representing the printed symbols has a high carbon content withinhibited infra red reflectivity (or enhanced absorption) betweenapproximately 750 nm and 1000 nm. Thus, the CCD of the camera is able todiscriminate between the printed and unprinted portions of the symboland to generate an image thereof. This image is fed to a “frame grabber”or other image capture device, and can then be fed to a PC24 or anotherdevice for storage and display. The image is now available as a computerimage file for decoding by suitable decoding software.

By utilising a suitable level of the encryption in the encoded datarepresented by the image, such as a multi-layer private/public keyencryption method, the data itself is adequately safeguarded againstattempts to decode or alter it. The present invention enhances thesecurity of such systems by preventing copying thereof.

Due to the large amount of light reflected by the background portion ofthe symbol, the CCD camera “sees” this portion of the image as white,whereas those parts which have conventional ink printed on them appearblack, and the two dimensional barcode image or symbol therefor isseparated or extracted from the background. However, since both inksappear black when illuminated by visible light, conventional imagingdevices such as scanners or photocopiers cannot extract the symbols fromthe background.

1. A method of generating a non-reproducible printed image on a documentincluding a conventionally printed image, the method comprising thesteps of: applying a first, background layer of a first ink that haslittle or no carbon content, which has a dark color and absorbs visiblelight but reflects light of a predetermined wavelength or range ofwavelengths, to a portion of a substrate in a preprocessing step; andprinting said conventionally printed image, and printing thenon-reproducible image on the background layer adjacent to saidconventionally printed image using a second ink that has a high carboncontent, which has a dark color that is visually indistinguishable fromthe first ink and absorbs both visible light and light of the wavelengthor range of wavelengths in a document printing step, wherein saidnon-reproducible image is substantially invisible relative to thebackground layer under visible light, copying of the document by aconventional imaging device utilizing visible light can reproduce saidconventionally printed image but cannot extract said non-reproducibleimage from the background layer, and the non-reproducible image becomesdiscernable by illumination of said non-reproducible image by light ofthe wavelength or range of wavelengths.
 2. A method according to claim 1wherein the wavelength or range of wavelengths is in the infraredspectrum.
 3. A method according to claim 2 wherein the first ink isreflective to light having a wavelength in the range of 850 nm to 900nm.
 4. A method according to claim 2 wherein the second ink is absorbentof light having a wavelength in the range 750 nm to 1000 nm.
 5. A methodaccording to claim 1 wherein the substrate comprises sheet material. 6.A method according to claim 5 wherein the substrate is a sheet of paper,a card, a tag, a label, a ticket, or an identification plate.
 7. Amethod according to claim 1 wherein the image is a bar-code or symbolicimage comprising computer-readable data.
 8. A method according to claim7 wherein the image is a two-dimensional encrypted bar-code or symbolicimage.
 9. Apparatus for reading a non-reproducible printed image printedby the method of claim 1, the apparatus comprising: a camera; a filterfor filtering an image captured by the camera at a predeterminedwavelength or range of wavelengths; and an illuminator arranged toilluminate the non-reproducible printed image with light at saidwavelengths or range of wavelengths, so that light reflected by thefirst, background layer of the printed image is passed by the filter,permitting reproduction of the image by the camera.
 10. Apparatusaccording to claim 9 wherein the filter comprises an infra red filterwhich passes infra red light and the illuminator comprises an infra redlight source.
 11. Apparatus according to claim 9 wherein the cameracomprises a CCD and generates a digitized image of the image. 12.Apparatus according to claim 9 including an image capture deviceconnectable to the camera for storing the digitized image andtransmitting the image to a computer.
 13. The method of claim 7, whereinthe image comprises encrypted data.
 14. The method of claim 13, whereinthe data has been processed by a forward error correction program thatadds parity information.
 15. The method of claim 14, wherein the data iscompressed prior to being processed by the forward error correctionprogram.
 16. The method of claim 15, wherein the compressed data thathas been processed by the forward error correction program in thenprocessed into symbols.
 17. The method of claim 16, wherein the symbolsare a set of ASCII strings.
 18. A method of generating anon-reproducible printed image on a document including a conventionallyprinted image, the method comprising the steps of: applying a first,background layer of a first ink that has little or no carbon content,which has a dark color and absorbs visible light but reflects light of apredetermined wavelength or range of wavelengths, to a portion of asubstrate in a preprocessing step; and printing said conventionallyprinted image, and printing the non-reproducible image on the backgroundlayer adjacent to said conventionally printed image using a second inkthat has a high carbon content, which has a dark color that is visuallyindistinguishable from the first ink when illuminated by visible lightand absorbs both visible light and light of the wavelength or range ofwavelengths, in a document printing step, wherein said non-reproducibleimage comprises encrypted data, and the non-reproducible image becomesdiscernable by illumination of said non-reproducible image by light ofthe wavelength or range of wavelengths.